How to display below layer's style

How to display below layer's style

Hi,
I'm new bee in geoserver,I have one question.
I have 3 layers on map,I had loaded first layer but on zoom layer 2 displayed at this time i want to display 1st layer's SLD as well as 2nd layer's SLD. How can I do that?

By Setting Opacity of polygon I can see below layer's label etc. but how can I display All Layer's Label?
I am really confuse on this,Can anyone help me on this please.